Gary N. Ervin

Wetlands and water quality in agricultural landscapes

Key Personnel

Gary Ervin, PI

Cory Shoemaker, Ph.D. (former doctoral student on the project)

Evelyn DiOrio (former Master's student on the project)

The research described here (funded largely through the USGS and the Mississippi Water Resources Research Institute) has sought to understand interactions between wetland function and wetland vegetation within the Mississippi Delta, an area of highly intensive agricultural land use.

During the years 2014-2017, we assessed vegetation, land use, soils, and water quality in and around 24 restored and 6 natural wetlands across a gradient of human land use in the Delta. This work encompassed observational studies within and around the wetlands themselves, as well as experimental work carried out on the MSU campus, looking at responses of seed banks and plant species to hydrology and inputs of nutrients and sediment.

Interest in, and rates of, wetland restoration have increased over the past several
decades. However, despite proliferations of restored wetlands across the landscape, the
structural and functional restoration success of these systems is unclear. Thus,
understanding factors and processes that influence wetland characteristics is of
considerable interest. This study focuses on herbaceous wetlands in the Mississippi River
Alluvial Valley (MAV), a largely agricultural region interspersed with restored and
naturally occurring wetlands.

This is a presentation that I gave in April 2017, at the Second University Congress of Agro-Food Sciences, in Mexico City. It's in Spanish, but an English-language abstract is:

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It is expected that intensification of agricultural activities will be required so that we can meet the needs of any estimated 9 billion people by the year 2050. Intensification of agriculture has the potential to affect the environment via nutrient and pesticide runoff, erosion, and soil salinization, among other potential impacts. Wetlands in agricultural landscapes face substantial challenges because of their frequent occurrence immediately adjacent to crops, but they also can serve an important role in mitigating agricultural impacts on downstream ecosystems. For example, wetlands can retain nutrients and sediments that would have been transported to streams, lakes, and nearshore costal environments, thus reducing impacts of eutrophication and hypoxia in coastal habitats, even when the wetlands themselves are located far inland. Our recent research has investigated the role of wetlands and wetland vegetation in mitigating impacts of agricultural practices, and we specifically have examined the relationship of wetland vegetation to nutrient and sediment contaminants. In our studies of wetlands that have been created or restored through federal conservation initiatives, we find that water quality is generally high in these wetlands, wetland species diversity appears to benefit from proximity to other land conservation practices, and plant assemblages of restored wetlands seem quite robust to inputs of nitrogen and sediment, within the range of those seen in intensely farmed landscapes. Our work thus has the potential to inform future restoration efforts within agricultural landscapes, which will be a critical need as we look to a future of providing food for a global population of 9 billion, while also maintaining adequate supplies of clean water for human use.

Studies have shown wetlands act as filters for nutrient rich waters, in part due to macrophyte properties. Differences have been found in nitrogen removal rates among plant species in studies of monocultures grown in mesocosms mimicking wastewater treatment constructed wetlands, but little research has been done on assemblages in natural or restored wetlands. This study aims to identify differences in water quality among plant assemblages in natural and restored wetlands. Thirty natural and restored wetlands in the Mississippi portion of the Mississippi Alluvial Valley were sampled four times. Water quality was measured and plant assemblages identified. Significant differences in pH, conductivity, and turbidity were found among four different plant growth forms, but nutrient concentrations were not significantly different among growth forms. Because nutrient concentrations were low, data collected may not have adequately captured potential differences in nutrient concentrations among plant assemblages.

Restoration of former agricultural lands to wetlands has increased in the past 25 years, with public and private programs subsidizing the conversion of marginal farmland into wetlands. These wetlands were constructed with structural and functional goals in mind, such as increasing biodiversity and water quality within local and regional watersheds. While successful in terms of area restored, restored wetlands frequently do not meet desired management goals; often, these wetlands resemble highly degraded wetlands in terms of structure and function, falling well short of management expectations. This study hypothesized that the deficiency between management goals and reality results from a lack of consideration of interactions among landscape attributes and local management practices. Together these factors may have substantial impacts on eventual structure and function of restored wetlands. To test this hypothesis, 24 restored wetlands enrolled in the Wetland Reserve Program (WRP) and six unmanaged, naturally occurring herbaceous wetlands were selected and surveyed in May and August of 2014. All sites were located in western Mississippi, USA, within the Mississippi Alluvial Valley. Wetland structure was assessed via percent cover of plant species, while functionality was represented by a suite of water quality parameters. Structurally, plant communities varied between managed and unmanaged sites, with unmanaged sites containing a greater cover of woody vegetation along with lower proportions of seed-bearing annuals. Land cover surrounding wetlands and throughout the study region was dominated by cultivated crops followed by emergent herbaceous wetlands, which were correlated with plant community composition and diversity. Nitrate (NO3-) and phosphate (PO43-) levels did not differ between managed and unmanaged sites, and were uncorrelated with variation in surrounding land cover. Continuing work is aimed at more detailed examinations of plant species assemblages responses to local land use and water quality parameters.